1. Field of the Invention
This invention relates to serial data decoding. More particularly, this invention relates to serial data decoding of a stream of variable length code words within which are imbedded control code words.
2. Description of the Prior Art
It is known to provide systems using streams of variable length codes to represent image data in a compressed form. An example of such a system is that proposed by the Joint Photographic Experts Group (JPEG). The JPEG system is primarily intended for use in compressing still images within general purpose computer systems. In such general purpose computer systems the necessary encoding and decoding can be performed with appropriate software. Whilst such an approach can be flexible and inexpensive, it will not be able to process data at a high enough rate to meet the requirements of providing real-time encoding and decoding of moving image data.
In order to meet this requirement dedicated hardware may be provided. British Patent Applications 9121122.7 and 9121123.5 (Sony Broadcast & Communications Limited) disclose one possible hardware decoder for serial data decoder for containing variable length codes. Although such hardware decoders provide high speed operation, they can be disadvantageously complex. One situation which can lead to such disadvantageous complexity is when control code words are embedded within the variable length code words. These control code words may be used to control the parameters by which the variable length code words are to be decoded. A hardware decoder capable of modifying its own operation in dependence upon decoded control code words whilst maintaining a high speed of operation would pose significant practical difficulties to implement.